The present invention relates generally to liquid crystal spatial light modulators, and more particularly to active matrix liquid crystal spatial light modulators.
Liquid crystal (LC) light modulators directly atop silicon integrated circuits form the basis of matrix addressed spatial light modulator (SLM) technology well suited to information display and optical information processing. This combination permits large arrays of compact "smart" pixels that can utilize the extensive repertoire of functionality available in extreme miniature on silicon VLSI (Very Large Scale Integrated) circuits. Devices made in this way can have array sizes up to 128.times.128 to 1000.times.1000, depending on the degree of pixel intelligence. They are similar in size and weight to an ordinary integrated circuit, and typically operate on low voltage (5 volt) power supplies, usually consuming less than 100 mW. The LC modulators of these arrays operate at conventional CMOS voltage levels, with update times as short as 100 micro seconds and efficient, high contrast modulation over wide wave length ranges.
One typical active matrix liquid crystal spatial light modulator in the prior art includes, among other components, a layer of liquid crystal material, for example ferroelectric liquid crystal material, which changes the way in which it acts on light in response to predetermined changes in voltage across the layer, whereby to modulate the light so acted upon. This layer of liquid crystal material is functionally divided into an array of adjacent pixel segments arranged in a predetermined way, typically in a matrix of rows and columns. An addressing scheme is provided for applying a voltage across this array of adjacent pixel segments and for individually modulating the voltage across each pixel segment in a controlled manner in order to modulate the light acted upon by the pixel segments in a correspondingly controlled way. In this typical active matrix liquid crystal spatial light modulator of the prior art, each pixel segment includes associated circuitry for modulating the voltage across the particular pixel segment, that is for changing its voltage, in response to a particular data or address voltage at the input of the circuitry.
A problem associated with the particular prior art device described immediately above resides in the fact that its addressing scheme is voltage limited, that is, the data or addressing voltages must be kept less than some maximum, for example 5 volts which is the standard in many integrated circuits. This is a result of many reasons including power dissipation problems associated with such devices.
As a result of this data or addressing voltage limitation just recited, the maximum voltage change that can possibly appear across the array of adjacent pixel segments making up the typical prior art active matrix liquid crystal spatial light modulator is correspondingly limited. That is, in such devices of the prior art, because the data or addressing voltage is by design limited to, for example, at most 5 volts, the voltage changes across the individual pixel segments (for modulating those segments) have been correspondingly limited to voltage changes somewhat smaller than the maximum data or addressing voltage levels, for example, somewhat less than 5 volts. Devices of the type to which the present invention is directed, for example active matrix ferroelectric liquid crystal spatial light modulators, could be speeded up and thereby improved upon if the voltage increase across the individual pixel segments could be increased without having to increase the data or addressing voltage and without creating power dissipation problems. As will be seen hereinafter, the present invention achieves just that by teaching a way to increase the maximum voltage change across each pixel segment to a level higher than the change of the data or addressing voltage.